EP0318434B1 - Extruder for manufacturing a plastic pipe - Google Patents

Abstract

To achieve a universal range of applications and at the same time greatly improved material utilisation, this plastics pipe (2) has a wall (1) of which the cross-section corresponds to an annularly bent double-web profile with hollow chambers (5) extending parallel to the longitudinal axis (4) of the pipe. <IMAGE>

Description

The invention relates to an extruder system for producing a plastic tube, the wall of which, viewed in cross section, has an annular multi-wall profile Corresponds to hollow chambers extending parallel to the longitudinal axis of the tube, the extruder head for producing the tubular profile being provided with a conical mandrel inside, the outer region of which is divided into a plurality of outer parts in a segment and finger-like manner according to the desired number of hollow chambers to be produced, and an at least approximately cylindrical one Surrounds the inner part with play that the outer parts and the inner part are provided with at least one opening each on their free end faces, which are connected to the outside atmosphere via the holder of the mandrel, and that the annular gap formed between the inner part and the outer parts is additionally on the entry side with the Outside of the mandrel communicates.

It is e.g. from FR-A-1 510 536 and EP-A-0 244 154 an extruder system of the type mentioned is known, which, however, have the disadvantage that the extruder head is designed in such a way that the extruded plastic material fed from the extruder over a relatively small feed cross-section is fed to the extruder head and then fed to the outer and inner annular gap via a flow cross-section which extends outward in the radial direction and thus (for geometric reasons with increasing radius) inevitably greatly increases.

In this way, in particular in the case of embodiments according to the prior art with relatively poorly flowing plastic material, it is not possible to achieve perfect filling of all the extruder head parts at higher production speeds.

The object of the present invention is to provide an extruder head which does not have these disadvantages.

According to the invention, this object is achieved according to claim 1.

According to the invention, the smallest inflow cross-section of an inflow chamber which leads to the outer annular gap, and thus inevitably the highest pressure in the plastic supplied, is located in the inlet area of the outer annular gap. The plastic required for the inner annular gap located on a smaller radius (= reduced flow cross-section) is branched off from this inlet area.

Such an embodiment according to the invention enables a perfect pipe quality even at high production speeds, which can be proven by practice.

To produce an at least partially heat-insulated plastic tube, it is advantageous if at least some of the outer parts are each provided with a feed channel for feeding a thermal insulation material into the hollow chambers to be formed.

Fig.1

eine Stirnansicht auf eine beispielsweise Ausführungsform eines erfindungsgemässen Kunststoff-Rohres;

Fig.2

eine Seitenansicht des in Fig. 1 dargestellten Kunststoff-Rohres;

Fig.3

einen teilweise im Schnitt dargestellten Extruderkopf einer erfindungsgemässen Extruderanlage;

Fig.4

eine Stirnansicht in Richtung des Pfeiles A in Fig. 3 auf den konischen Dorn;

Fig.5

einen Schnitt längs der Linie V-V in Fig. 4 durch den konischen Dorn; und

Fig.5a

in vergrössertem Massstab eine alternative Ausführungsform eines Details des in Fig. 5 dargestellten Dornes.

The invention is explained in more detail below on the basis of an exemplary embodiment shown in the drawing. It shows:

Fig. 1

an end view of an example embodiment of a plastic tube according to the invention;

Fig. 2

a side view of the plastic tube shown in Fig. 1;

Fig. 3

an extruder head partially shown in section of an extruder system according to the invention;

Fig. 4

an end view in the direction of arrow A in Figure 3 on the conical mandrel.

Fig. 5

a section along the line VV in Figure 4 by the conical mandrel. and

Fig.5a

on an enlarged scale, an alternative embodiment of a detail of the mandrel shown in FIG. 5.

As can be seen in particular from FIGS. 1 and 2, the wall 1 of the plastic pipe 2 according to the invention, viewed in cross section, has a double web profile 3 which is curved in the form of an annular ring and has hollow chambers 5 which extend parallel to the pipe longitudinal axis 4. When viewed in cross section, the individual chambers 5 have at least approximately the shape of a circular ring segment.

If a well-insulated pipe 2 is to be produced, then it is possible to manufacture the pipe 2 with the hollow chambers 5 to be filled in simultaneously with a thermal insulation material, for example polystyrene foam.

An extrusion process is used to produce this plastic tube 2. The extruder system to be used (not shown), which can be of known conventional design, has an extruder head 6 as shown in FIGS. 3 to 5.

As can be seen in particular from FIGS. 3 to 5, the extruder head 6 is provided with a conical mandrel 7 to produce the tubular profile shown in FIGS. 1 and 2, the outer region of which, according to the number of hollow chambers 5 to be produced, is segmented and finger-like into one A plurality of outer parts 8 is divided, and surrounds a cylindrical inner part 9 with a game s corresponding to the desired wall thickness.

In order to avoid a collapse of the cavities 5 and 11 formed in this way, or of the tube profile thus extruded, before the extruded material cools and solidifies sufficiently, the outer parts 8 and the inner part 9, as can be seen in FIGS. 4 and 5, are also provided on their free end faces each have at least one opening 12 or 13, which are connected via the channels 14, 15, 16 and 17 to the outside atmosphere, from where air is automatically sucked into the hollow chambers 5 being formed.

The outer parts 8 are laterally separated from one another by gaps 18 running in radial planes, the width b of which corresponds to the thickness of the tube wall webs 19 to be produced.

In order to ensure that the liquid plastic to be processed runs smoothly from the extruder 20 into between the inner part 9 and the outer parts 8 to form the annular gap 21, the latter, in addition to the gaps 18, is additionally on the inlet side via feed bores 22 which run obliquely backwards and outwards between the individual outer parts 8 and whose diameter is at least twice, preferably at least three times as large as the gap width b is connected to the outside of the mandrel 7.

A heating arrangement 24 is provided on the outside of the extruder head 6.

If a hollow chamber 5 is sometimes to be simultaneously filled with a thermal insulation material during the manufacture of the tubular profile, then it is expedient if, as can be seen from FIG. 5a, the outer part 8 used to form this hollow chamber 5 has a supply channel 23 for supplying a thermal insulation material into it hollow chamber 5 to be formed is provided. If the hollow chambers 5 are always to be foamed with a thermal insulation material, then the air supply channels 14 in the outer parts 8 can even be omitted entirely.

A pipe 2 designed according to FIGS. 1 and 2 can be used, for example, as an electrical installation pipe. This pipe according to the invention offers, with almost the same amount of material as before, a considerably improved mechanical protection of the electrical cables drawn through such a pipe against damage to the latter, which is particularly important in the case of buried installation pipes.

In house installations, it is also possible, for example, to insert one or more 380V cables through the inner pipe duct 11, one or more 220V cables through one or more of the outer pipe ducts 5, and through one or more of the rest Pipe channels 5 to lead one or more low-voltage cables, all spatially separated.

A pipe 2 designed according to FIGS. 1 and 2 can of course also be used for the passage of gaseous and / or liquid media. It is possible, for example, to pass a first liquid through the inner pipe duct 11 and through at least a part of the outer pipe ducts 5, in the same or opposite direction, with the same or different temperature, at least one further liquid and / or a gas. In this way, the tube 2 can also serve as a heat exchanger.

To form a heat-insulated pipe 2, it is also possible to fill the outer pipe channels 5 with a heat-insulating material, for example with polystyrene foam, during the extrusion of the pipe profile.

Of course, it is also possible, with a suitable choice of material, to use the tube 2 according to the invention as a dimensionally stable component, for example for masts, scaffolding or other tube structures.

It is also possible to use the same principle to e.g. with a three-rib profile, i.e. to form two rows of hollow chambers arranged concentrically to one another.

Claims (2)

1. Extruder for the manufacture of a plastic pipe, the wall of which, when considered from its cross section, corresponds to an annular bent multiple web profile with hollow chambers (5) located parallel to the longitudinal axis of the pipe (4), whereby for the production of the pipe profile the inside of the extruder head (6) has been provided with a conical mandrel (7), the outer area of which corresponding to the requested number of hollow chambers (5) to be produced is divided up into a multitude of external parts (8) shaped like segments and fingers, which surrounds an almost cylindrical internal port (9) with play in such a way that the free face of the external parts (8) as well as of the internal part (9) is provided with at least one opening each (12, 13) which is linked to the outside atmosphere by the holding device of the mandrel (7), and in such a way that the annual gap (21) formed between the internal part (9) and the external parts (8) is linked on the entry side with the outside of the mandrel (7) in addition characterised by the fact that the entry side of the extruder head (6) has been provided with an inflow chamber (25), the outside (26) of which corresponds to the surface area of a regular cylinder (26) with a radius (R) identical with the outside radius of the pipe to be produced, and the inside (27) of which is shaped in such a way that the flow-through cross section of this chamber (25) in flow direction decreases continuously and feed boreholes (22), which run between the individual segment and finger like external parts (8) leading from the outside of the mandrel (7) to its inside, have been provided for entry side connection of the inner annual gap (21) with this chamber (25) directly before reaching the narrowest flow through cross section of this chamber corresponding to the annular thickness (t) of the annular external pipe part (28), whereby the diameters of the feed boreholes on the entry side are larger than the lateral gap width (b) between the individual finger-like external parts (8).
2. Extruder as set forth in claim 1 characterised by the fact that at least some of the external parts (8) are provided with a feed channel (23) each for the insertion of a heat insulator into the hollow chambers (5) to be produced.

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